Emulsions

ABSTRACT

The invention provides a water/oil/water duplex emulsion in which the external continuous phase is gelled. This gelling is obtained by having an osmotic pressure component, e.g. an electrolyte, in the internal aqueous phase which draws water from the external phase through the oil phase. The structure is firm but contains a considerable volume of available aqueous phase. The structure is of value in e.g. foods and cosmetics.

FIELD OF THE INVENTION

This invention relates to duplex emulsions of the water/oil/water (WOW)type. Emulsions of this class comprise an aqueous phase dispersed in anoil phase which is, in turn, within an outer continuous aqueous phase.Such systems are also termed multiple emulsions. These systems haveutility in e.g. foods, drug deliveries, creams and cosmetics intendedfor topical application.

BACKGROUND TO THE INVENTION

Water/oil/water emulsions have been available for many years and it hasbeen appreciated they can provide release systems, eg. for perfumes,cosmetic active ingredients and flavours, and control of rheology.

GENERAL DESCRIPTION OF THE INVENTION

The invention provides a gelled duplex emulsion structure comprising

(i) 0.1% to about 40% by weight of a gelled external

continuous aqueous phase,

(ii) oil or substantially liquid fat component, preferably edible,dispersed in the external phase and

(iii) an aqueous phase containing an osmotic pressure component anddispersed in the oil or substantially liquid fat phase.

The duplex emulsion structure is thus characterized by having a gellingcomponent in the external aqueous phase and an osmotic pressurecomponent in the internal aqueous phase. In the product the gelledexternal phase preferably forms at least 1% of the structure andpreferably up to about 20% by weight. The oil/fat phase will usuallyform from about 5% to about 30% by weight of the total composition,preferably from about 10% to about 20%.

In these novel gel structures droplets of a free aqueous solution areretained within a three dimensional gel network. This structure isobtained with low levels of a gelling component because the latter ispresent as a concentrated gel in the lamellae between the droplets ofthe swollen w/o emulsion, thus forming a three dimensional networkthrough the structure. Thus a structure containing a high proportion ofungelled aqueous solution is provided. The concentration of gellingcomponent in the lamellae is relatively high although the initialexternal aqueous phase has a lower concentration. Usually the claimedcombination of gelling agent and swelling duplex emulsion provide agelling time from a few minutes to several hours. Thus a structure isprovided which is formed in situ to give a firm structure with arelatively high volume of available dispersed liquid phase.

Preferably the external continuous aqueous phase also contains anosmotic pressure component to control the rate of osmosis until osmoticbalance is achieved. The presence of an external osmotic pressurecomponent allows the progress to osmotic balance to be controlled moreexactly. The gel structure obtained is effective even if in time thetotal structure forms a network in which some of the discrete volumeswithin the gel become connected as the gel membranes between thembreakdown.

A fat component is usable, but in this duplex form the emulsion would beformed above the fat melting point, where the phase is substantiallyliquid, and retained there while osmosis and gelling occurred. The finalstructure would, in this case, comprise a solid fat phase formed as thegelled structure is cooled to ambient.

In one embodiment of the structure reactive species can be retainedseparate as different aqueous solutions in internal aqueous phases.These species are brought into contact to produce, eg. a colour change,when the gel structure is ruptured.

Thus the invention includes a method of preparing a gelled duplexemulsion structure wherein a water in oil/fat emulsion, having anosmotic pressure component in the aqueous phase, is dispersed in asolution of a gelling component, preferably containing about 0.1% toabout 5%, usually up to about 2% by weight of the component, and theemulsion retained until the external continuous phase has gelled.

Gelling of the external aqueous phase can be achieved by release of asolute from the internal aqueous phase. Speed of release and thusgelling is dependent, inter alia, on the size of internal aqueous andoil droplets, concentration gradient across the oil membrane andemulsifier concentrations. Thus control of gelling is obtained byvarying these features. The term "gelling" is used herein to includephysical setting by thermal or chemical means.

Osmotic swelling of the water in oil emulsion in the systems of theinvention prepared from (i) self gelling components and (ii) thoserequiring cation release causes the gelling component to be increased inconcentration. However for cation sensitive gelling the major factor ingelling is the controlled release of the cation from the internal waterphase, although an increase in concentration of the gelling componentalso occurs.

Further control of the swelling and release rates can be obtained byhaving a separate osmotic swelling component in the droplets from whichthe desired component is to be released to cause gelling of the externalphase. That is, the internal aqueous phase can comprise two types ofdroplets.

COMPONENTS OF THE INVENTION

The internal aqueous phase containing the osmotic pressure component isdispersed in the oil/fat phase which is, in turn, dispersed in theexternal continuous phase containing the gelling component.

Examples of the oils and fats are olive oil, palm oil, groundnut oil,sunflower oil and animal fats, for example tallow and lard.

An internal emulsifier is required to stabilize the water in oilemulsion and will normally have a hydrophilic-lipophilic balance (HLB)of not more than 6, preferably not more than 5. Examples of theseemulsifiers are the polyglycerol esters of fatty acids, optionallypolymerized fatty acids. Another suitable emulsifier is polyglycerolpolyricinoleic acid obtainable from Quest International Limited ofAshford, England under the trade name Admul WOL. Other examples ofemulsifiers are sorbitan mono-oleate and analagous esters, sucroseesters and lecithin dependent on the other components. Alternatively theinternal phase may be stablilized by solid particles with appropriatesurface properties which move to the W/O interface. The internalemulsifier is capable of stabilizing the water/oil emulsion in the firstemulsion stage when the oil containing the dispersed aqueous phase isemulsified in the external aqueous phase.

The external oil/water emulsifier will normally have an HLB of at least8 and examples are polyoxyethylene sorbitan esters. Other emulsifiersare proteins, for example milk proteins, blood proteins and eggproteins. The emulsifier stabilises the oil droplets as a dispersion inthe continuous aqueous phase. Other materials usable as the external o/wemulsifier are diacetyl tartaric acid esters of monoglycerides (E472E),sucrose esters and stearoyl lactylates.

The internal aqueous phase is required to include an osmotic pressurecomponent which generates an osmotic gradient between the internal andexternal aqueous phases. This osmotic pressure component will be watersoluble with a relatively low oil solubility. Examples of this componentare salts, eg. sodium chloride, sugars, for example glucose, sucrose andmalto-dextrins; other solutes are amino acids and peptides. Urea, acomponent of value in skin humectant compositions, may also be used.

The gelling component in the external continuous phase is required toform a gel because its concentration increases with movement of waterthrough the oil/fat semi-permeable membrane or be gelled during or afterbeing concentrated by this process by any conventional gelling processwhich may be brought about by, for example, cooling, heating or chemicalreaction. Gelling may be accelerated or achieved by interaction with anappropriate cation released from the internal aqueous phase. Examples ofthe gelling component are gelatin and meat, egg and fish proteins,gelling polysaccharides, for example, xanthan/galactomannan mixtures,k-carrageenan/potassium and alginate/calcium. Additionally particulateinorganic materials, e.g. laponite clays, are usable as the gellingcomponent.

SPECIFIC DESCRIPTION OF THE INVENTION

Examples of the duplex emulsions of the invention will now be given toillustrate but not limit the invention.

EXAMPLE I

Examples of four duplex emulsions of the invention were prepared andtheir compression characteristics compared with an oil in water emulsionof the same overall composition.

In these formulations the external continuous aqueous phase had theinitial composition (w/w):

    ______________________________________                                        sodium caseinate  1%                                                          gelatin (250 Bloom)                                                                             1%                                                          sucrose           1%                                                          water             97%                                                         ______________________________________                                    

The caseinate functions as the oil in water emulsifier.

Two water in oil emulsions A and B were prepared by emulsifying 30 g ofa sucrose solution into groundnut oil (50 g) with the aid of Admul WOL(5 g) as emulsifier. The latter is polyglycerol polyricinoleic acidobtainable from Quest International of Ashford England. Emulsificationwas achieved using a Silverson mixer (type L2R) on full power with afine emulsor screen for 5 minutes. The two emulsions differed by theconcentration of sucrose in the aqueous solution. Solution A contained30% w/w sucrose and solution B was 70% w/w sucrose.

Four duplex emulsions were prepared by emulsifying two amounts ofemulsions A and B into the external phase solution by gently shearingwith a Silverson mixer at low (1/4) power for 10 to 40 secs. Forpurposes of comparison equivalent amounts of groundnut oil wereemulsified into the external phase solution to provide oil in watersingle emulsions. The sucrose component acted to draw water from thecontinuous phase into the internal aqueous phase through the oil layerunder osmotic drive.

The initial phase volumes of the w/o emulsion is approximately in therange 0.2-0.3. After osmotically driven swelling of the internal aqueousphase these formulations theoretically produce disperse phase volumesapproximately in the range 0.7-0.9. However, in practice, a smallproportion of the internal phase is lost in preparation and duringosmotic swelling so the actual volume of dispersed phase is somewhatlower than calculated theoretically.

These six emulsions were prepared at 45° C., poured into moulds andallowed to set overnight (8-16 hrs) at 5° C. The four duplex emulsionsset more rapidly than the two single emulsion comparisons and a sampleof the external phase.

The compression characteristics of the gelled materials was tested usingan Instron compression tester at 5° C. The results, given in Table I,demonstrate the duplex emulsions of the invention provide stronger gels.The force (Newtons) registered when a sample was compressed to 50% oforiginal height was noted.

                  TABLE I                                                         ______________________________________                                               Physical  External Internal   Force                                    Example                                                                              Form      Phase    Phase      (Newtons)                                ______________________________________                                        I      duplex    200 g    Emulsion A 0.433                                                              50 g                                                2      duplex    200 g    Emulsion B 0.400                                                              50 g                                                3      duplex    200 g    Emulsion A 0.367                                                              75 g                                                4      duplex    200 g    Emulsion B 0.463                                                              75 g                                                5*     oil in    200 g    Groundnut Oil                                                                            0.116                                           water              29 g                                                6*     oil in    200 g    Groundnut Oil                                                                            0.125                                           water              44 g                                                7*     solution  (external phase)  0.056                                      ______________________________________                                         *Comparison                                                              

So as to further indicate the novel properties of cellular gels theviscoelastic behaviour has been compared with simple gels of the sameoverall composition (excluding the w/o emulsifier and the sucrosecomponent of the internal water phase). The formulations are shownbelow:

External Phase(s)

    ______________________________________                                        Sodium caseinate       1 g                                                    Sucrose                1 g                                                    Gelatin                0.3, 0.6, 1 g                                          Water                  to 100 g                                               ______________________________________                                    

Internal Phase(s)

    ______________________________________                                        Ground nut oil         50 g                                                   Admul WOL              5 g                                                    Sucrose solution (30% w/w)                                                                           30 g                                                   ______________________________________                                    

Measurements were made at 0.1 hertz after setting at 5° C. for 1 hour.The results are given in Table II.

It is clear that the elastic modulus of these gelled emulsions is verymuch higher at a given gelatin concentration than the gel formed fromthe o/w emulsion of similar composition. Secondly, the phase angle (d)is much larger for these gels than for the equivalent gelled oil inwater emulsions. The ratio of the loss to storage modulus (tan d) ismuch larger for these gels, indicating them to have additional energydissipation modes. These presumably include the viscous flow of liquidinside the swollen duplex droplets.

                                      TABLE II                                    __________________________________________________________________________                                 ELASTIC                                                                              LOSS                                             PHYSICAL                                                                             EXTERNAL                                                                             DISPERSED                                                                             MODULUS                                                                              MODULUS                                   EXAMPLE                                                                              FROM   PHASE  PHASE   (Nm.sup.-2)                                                                          (Nm.sup.-2)                                                                          d TAN d                            __________________________________________________________________________    8      Duplex 200 g - 0.3%                                                                         75 g w/o                                                                              33.6   13.6   22                                                                              0.404                                          gelatin                                                         9      Duplex 200 g - 0.6%                                                                         75 g w/o                                                                              401    85.2   12                                                                              0.213                                          gelatin                                                         10     Duplex 200 g - 1%                                                                           75 g w/o                                                                              863    136.7   9                                                                              0.158                                          gelatin                                                         11*    o/w    200 g - 0.3%                                                                         44 g oil                                                                              no gel no gel --                                                                              --                                             gelatin                                                         12*    o/w    200 g - 0.6%                                                                         44 g oil                                                                              1.24   0.26    4                                                                              --                                             gelatin                                                         13*    o/w    200 g - 1.0%                                                                         44 g oil                                                                              25.3   1.77    4                                                                              --                                             gelatin                                                         __________________________________________________________________________     *Comparison                                                              

EXAMPLE II

A series of w/o emulsions were prepared by emulsifying an aqueoussolution (A) (50 g) into groundnut oil (50g) using of Admul WOL (3 g) asemulsifier. Solution A contained sucrose (30% w/w) and variousconcentrations of KCl in the range 0.3% w/w to 3.0% w/w.

Emulsification was accomplished using a Silverson mixer under theconditions of example I. Three duplex emulsions were prepared at eachpotassium chloride level by emulsifying the water in oil emulsion (50 g,70 g, 90 g) into 200 g of the external phase (B) at 25° C. using aSilverson mixer under the mild conditions of Example I.

The external phase (B) had the composition.

    ______________________________________                                        Sucrose                 2 g                                                   Sodium Caseinate        2 g                                                   K Carrageenan (L100)    2 g                                                   Distilled water         194 g                                                                         200 g                                                 ______________________________________                                    

The duplex emulsion formed was stirred with a magnetic stirrer at slowspeed until gelation occurred.

Similarly to example I the initial phase volumes of the w/o lay in therange 0.2-0.35. Simple osmotically driven swelling of the internal waterphase would produce dispersed phase volumes in the appropriate rangeabout 0.7-about 0.9. However, the release of some of the internal phaseduring preparation and osmotic swelling reduces the actual dispersephase volumes after swelling to less than this theorectical maximum.

The results are given in Table III (amounts w/w).

                                      TABLE III                                   __________________________________________________________________________                         KCl CONC                                                               DISPERSE                                                                             % W/W IN                                                        EXTERNAL                                                                             PHASE  DISPERSED  GELLING                                       EXAMPLE                                                                              PHASE  (W/O)  WATER PHASE                                                                              TIME                                          __________________________________________________________________________    14     200 g  50 g   3          7-8  mins                                     15     200 g  70 g   3          5-6  mins                                     16     200 g  90 g   3          2-3  mins                                     17     200 g  50 g   1          >120 mins                                     18     200 g  70 g   1          about 40                                                                           mins                                     19     200 g  90 g   1          about 20                                                                           mins                                     20     200 g  50 g   0.3                                                      21     200 g  70 g   0.3        several hrs                                   22     200 g  90 g   0.3                                                      __________________________________________________________________________

THe gelled emulsion obtained under the conditions described abovedepends both on the swelling of the duplex droplets, to produce a highdisperse phase volume, and on the release of potassium from some of thedroplets. More independent control of the potassium release and theswelling is obtained when the sucrose and potassium are incorporated inseparate droplets.

We claim:
 1. A gelled duplex emulsion structure consisting essentiallyof:(i) 0.1% to about 40% by weight of a gelled external continuousaqueous phase comprising a gelling component selected from gelatin,meat, egg protein, fish protein, gelling polysaccharides and clays; (ii)oil or liquid fat component from about 5% to about 30% by weightselected from olive oil, palm oil, groundnut oil, sunflower oil andanimal fats dispersed in the external phase; (and) (iii) an aqueousphase containing an osmotic pressure component selected from peptidesand urea and dispersed in the oil or fat phase- (iv) an internalemulsifier in a sufficient amount to stabilize the water in oil emulsionhaving a hydrophilic-lipophilic balance (HLB) of not more than 6 and (v)a sufficient amount of an external oil/water emulsifer having an HLB ofat least
 8. 2. A gelled duplex emulsion structure according to claim 1wherein the gelled external continuous aqueous phase forms at least 1%by weight of the structure.
 3. A gelled duplex emulsion structureaccording to claim 1 or 2 wherein the gelled external continuous aqueousphase forms up to about 20% by weight of the structure.
 4. A gelledduplex emulsion structure according to claim 1, wherein the oil/fatcomponent forms from about 10% by weight to about 20% by weight.
 5. Agelled duplex emulsion structure according to claim 1 wherein thetheoretical disperse phase volume is in the range about 0.7 to about0.9.
 6. A method of preparing a gelled duplex emulsion structureaccording to claim 1, wherein an emulsion of water in an oil or liquidfat selected from olive oil, palm oil, groundnut oil, sunflower oil andanimals fats, having in the aqueous phase an osmotic pressure componentselected from peptides and urea is dispersed in an aqueous solution of agelling component selected from gelatin, meat, egg protein, fishprotein, gelling polysaccharides and clays, causing the externalcontinuous phase to gel by thermal or chemical means and the emulsion isretained until the external continuous phase has gelled.
 7. A method ofpreparing a gelled duplex emulsion structure as claimed in claim 6wherein the initial external phase contains from about 0.1% to about 5%by weight of gelling component.